Field of the Invention
The present invention relates to a zoom lens, and more particularly, to a zoom lens suitable as an image pickup optical system to be used in an image pickup apparatus, such as a monitoring camera, a digital camera, a video camera, and a broadcasting camera.
Description of the Related Art
In recent years, as an image pickup optical system to be used in an image pickup apparatus, a zoom lens is required to have a wide field angle and a small overall system size. For example, as an image pickup optical system to be used for a monitoring camera, a zoom lens is required to have a wide field angle and a small overall system size, and is also required that favorable optical characteristics can be obtained in imaging during daytime and at night.
In general, a monitoring camera uses visible light in imaging during daytime, and uses near-infrared light in imaging at night. The use of near-infrared light provides an advantage in that imaging can be carried out with less influence of scattering than when visible light is used, for example, in a dense fog with low visibility. Thus, it is demanded that a zoom lens used in a monitoring camera be corrected for an aberration in a broad wavelength range from a visible range to a near-infrared range.
In the related art, as the zoom lens for the monitoring camera, a two-unit zoom lens including, in order from an object side to an image side, a first lens unit having a negative refractive power, an aperture stop, and a second lens unit having a positive refractive power has been known. In a zoom lens disclosed in each of Japanese Patent No. 5806299, Japanese Patent Application Laid-Open No. 2011-175174, and Japanese Patent Application Laid-Open No. 2009-230122, an interval between the first lens unit and the second lens unit in an optical axis direction is changed to vary a magnification, and the first lens unit is moved to correct an image plane variation accompanying the magnification varying.
In the zoom lens for a monitoring camera, in order to obtain favorable optical characteristics over a broad wavelength range from a visible range to a near-infrared range, it is important to appropriately set the zoom type and the lens configuration of each lens unit. For example, in a zoom lens formed of at least two lens units including, in order from an object side to an image side, a first lens unit having a negative refractive power, and a second lens unit having a positive refractive power, it is important to appropriately set the second lens unit to satisfactorily correct chromatic aberration over a wide wavelength range.